Fault detection in a cooling system with a plurality of identical cooling circuits

ABSTRACT

In a cooling system having a plurality of identical cooling circuits, fault detection is determined by a controller if monitored operating parameters of the cooling circuits differ from each other by an appreciable amount. In an aspect, the controller uses a comparison of the operating parameters of a cooling circuit to a snapshot of the operating parameters of that cooling circuit taken after the cooling circuit is determined to be operating properly after start-up. In an aspect, the controller uses known operating parameters of a cooling circuit and a system model of the cooling circuit to calculate remaining operating parameters of the cooling circuit (system model operating parameters) and uses a comparison of the system model operating parameters to the monitored operating parameters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/734,414 filed on Dec. 7, 2012. The entire disclosure of the above application is incorporated herein by reference.

FIELD

The present disclosure relates to detecting faults in a cooling circuit of a cooling system.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

Cooling systems have applicability in a number of different applications where fluid is to be cooled. They are used in cooling gas, such as air, and liquids, such as water. Two common examples are building HVAC (heating, ventilation, air conditioning) systems that are used for “comfort cooling,” that is, to cool spaces where people are present such as offices, and data center climate control systems.

A data center is a room containing a collection of electronic equipment, such as computer servers. Data centers and the equipment contained therein typically have optimal environmental operating conditions, temperature and humidity in particular. Cooling systems used for data centers typically include climate control systems, usually implemented as part the control for the cooling system, to maintain the proper temperature and humidity in the data center.

FIG. 1 shows an example of a typical data center 100 having a climate control system 102 (also known as a cooling system). Data center 100 illustratively utilizes the “hot” and “cold” aisle approach where equipment racks 104 are arranged to create hot aisles 106 and cold aisles 108. Data center 100 is also illustratively a raised floor data center having a raised floor 110 above a sub-floor 112. The space between raised floor 110 and sub-floor 112 provides a supply air plenum 114 for conditioned supply air (sometimes referred to as “cold” air) flowing from computer room air conditioners (“CRACs”) 116 of climate control system 102 up through raised floor 110 into data center 100. The conditioned supply air then flows into the fronts of equipment racks 104, through the equipment (not shown) mounted in the equipment racks where it cools the equipment, and the hot air is then exhausted out through the backs of equipment racks 104, or the tops of racks 104. In variations, the conditioned supply air flows into bottoms of the racks and is exhausted out of the backs of the racks 104 or the tops of the racks 104.

It should be understood that data center 100 may not have a raised floor 110 nor plenum 114. In this case, the CRAC's 116 would draw in through an air inlet (not shown) heated air from the data center, cool it, and exhaust it from an air outlet 117 shown in phantom in FIG. 1 back into the data center. The CRACS 116 may, for example, be arranged in the rows of the electronic equipment, may be disposed with their cool air supply facing respective cold aisles, or be disposed along walls of the data center.

In the example data center 100 shown in FIG. 1, data center 100 has a dropped ceiling 118 where the space between dropped ceiling 118 and ceiling 120 provides a hot air plenum 122 into which the hot air exhausted from equipment racks 104 is drawn and through which the hot air flows back to CRACs 116. A return air plenum (not shown) for each CRAC 116 couples that CRAC 116 to plenum 122.

CRACs 116 may be chilled water CRACs or direct expansion (DX) CRACs. CRACs 116 are coupled to a heat rejection device 124 that provides cooled liquid to CRACs 116. Heat rejection device 124 is a device that transfers heat from the return fluid from CRACs 116 to a cooler medium, such as outside ambient air. Heat rejection device 124 may include air or liquid cooled heat exchangers. Heat rejection device 124 may also be a refrigeration condenser system, in which case a refrigerant is provided to CRACs 116 and CRACs 116 may be phase change refrigerant air conditioning systems having refrigerant compressors, such as a DX system. Each CRAC 116 may include a controller 125 that controls the CRAC 116. Controller 125 may illustratively be an iCOM® control system available from Liebert Corporation of Columbus, Ohio.

In an aspect, CRAC 116 includes a variable capacity compressor and may for example include a variable capacity compressor for each DX cooling circuit of CRAC 116. It should be understood that CRAC 116 may, as is often the case, have multiple DX cooling circuits. In an aspect, CRAC 116 includes a capacity modulated type of compressor or a 4-step semi-hermetic compressor, such as those available from Emerson Climate Technologies, Liebert Corporation or the Carlyle division of United Technologies. CRAC 116 may also include one or more air moving units 119, such as fans or blowers. The air moving units 119 may be provided in CRACs 116 or may additionally or alternatively be provided in supply air plenum 114 as shown in phantom at 121. Air moving units 119, 121 may illustratively have variable speed drives.

A typical CRAC 200 having a typical DX cooling circuit is shown in FIG. 2. CRAC 200 has a cabinet 202 in which an evaporator 204 is disposed. Evaporator 204 may be a V-coil assembly. An air moving unit 206, such as a fan or squirrel cage blower, is also disposed in cabinet 202 and situated to draw air through evaporator 204 from an inlet (not shown) of cabinet 202, where it is cooled by evaporator 204, and direct the cooled air out of plenum 208. Evaporator 204, a compressor 210, a condenser 212 and an expansion valve 214 are coupled together in known fashion in a DX refrigeration circuit. A phase change refrigerant is circulated by compressor 210 through condenser 212, expansion valve 214, evaporator 204 and back to compressor 210. Condenser 212 may be any of a variety of types of condensers conventionally used in cooling systems, such as an air cooled condenser, a water cooled condenser, or glycol cooled condenser. It should be understood that condenser 210 is often not part of the CRAC but is located elsewhere, such as outside the building in which the CRAC is located. Compressor 210 may be any of a variety of types of compressors conventionally used in DX refrigeration systems, such as a scroll compressor. When evaporator 204 is a V-coil or A-coil assembly, it typically has a cooling slab (or slabs) on each leg of the V or A, as applicable. Each cooling slab may, for example, be in a separate cooling circuit with each cooling circuit having a separate compressor. Alternatively, the fluid circuits in each slab such as where there are two slabs and two compressor circuits, can be intermingled among the two compressor circuits.

The cooling circuits may be other than DX cooling circuits. They may for example be pumped refrigerant cooling circuits, chilled water cooling circuits, or cooling circuits having both a DX mode and a pumped refrigerant mode.

Controller 125 will typically include fault detection to detect whether there has been a failure of the cooling system including the cooling circuit (or circuits) that the controller 125 is controlling. Such fault detection has typically been on an individual cooling circuit basis. That is, one or more operating parameters of an individual cooling circuit are monitored by controller 125 and if they deviate sufficiently from a setpoint, or are outside of a set range, the controller determines that a fault has occurred in the cooling circuit. The setpoint or set range may for example, as the case may be, can be fixed, user input, or dynamically determined.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

A cooling system in accordance with an aspect of the present disclosure has a plurality of identical cooling circuits and a controller that controls the cooling circuits. The controller includes fault detection to detect whether there has been a failure of any of the cooling circuits that it is controlling. In an aspect, the fault detection includes the controller monitoring the operating parameters of each of the cooling circuits and comparing operating parameters of one cooling circuit to operating parameters of the other cooling circuit. If corresponding operating parameters of the cooling circuits differ from each other by an appreciable amount, the controller determines that a fault has occurred.

In an aspect, the controller determines possible causes of a fault that occurred based on the comparison of corresponding operating parameters of the cooling circuits and which differ from each other by an appreciable amount and which do not. In an aspect, the controller outputs a response based on the determined possible causes of the fault.

In an aspect, the controller uses a comparison of the operating parameters of a cooling circuit to a snapshot of the operating parameters of that cooling circuit taken after the cooling circuit is determined to be operating properly after start-up, which is referred to herein as the original snapshot. The controller makes this comparison when the cooling circuit is operating at a similar condition to when the original snapshot was taken.

In an aspect, the controller calculates uses known operating parameters of a cooling circuit as inputs to a system model and uses the system model to calculate remaining operating parameters of the cooling circuit (collectively, the system model operating parameters) and uses a comparison of the system model operating parameters of the cooling circuit to monitored parameters of the cooling circuit.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic illustrating a prior art data center;

FIG. 2 is a simplified perspective view of a prior art CRAC having a DX cooling circuit;

FIG. 3 is a schematic showing a CRAC having two DX cooling circuits;

FIG. 4 is a spreadsheet listing failure modes and the relationship of particular operating parameters of the cooling circuits on which of the failure modes is determined;

FIG. 5 is a schematic showing a cooling system having two cooling circuits with each cooling circuit include a DX mode and a pumped refrigerant economizer mode;

FIG. 6 is a basic flow chart of a software program for fault detection in accordance with an aspect of the present disclosure;

FIG. 7 is a basic flow chart of a software program for fault detection in accordance with an aspect of the present disclosure; and

FIG. 8 is a basic flow chart of a software program for fault detection in accordance with an aspect of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

FIG. 3 is a simplified schematic of a cooling system 300 having a plurality of cooling circuits 302, such as may be utilized for CRAC 200 with each cooling circuit 302 being the cooling circuit for one of the legs of the A or V coil assembly (as applicable). Cooling circuits 302 are both DX refrigeration circuits that are identical to each other and include evaporator 204, compressor 210, condenser 212 and expansion valve 214. In this context, cooling circuits 302 being identical to each other means that their functional components (compressors, expansion valves, heat exchangers, evaporators, condensers, refrigerant charge quantity, piping, fans, etc.) that physically make up the refrigerant circuit and the conditions (indoor air temperature, outdoor air temperature, indoor air flow, outdoor air flow, etc.) are by design the same (equal) in form, fit, function, and performance and thus should perform essentially the same within measurement tolerances. Cooling system 300 includes controller 320 that controls cooling circuits 302. Controller 320 may include, or be coupled to, a user interface 321. Expansion valves 214 may preferably be electronic expansion valves, but may also be thermostatic expansion valves such as those disclosed in U.S. Pat. No. 4,606,198. In each DX refrigeration circuit 302, a refrigerant is circulated by the compressor and it flows from the compressor, through the condenser, expansion valve, evaporator and back to the compressor. It should be understood that each compressor 210 may include tandem compressors with one compressor a fixed capacity compressor and the other compressor a variable capacity compressor, such as a digital scroll compressor. Each compressor 210 may be a tandem digital scroll compressor that includes a fixed capacity scroll compressor and a digital scroll compressor. It should be understood that cooling circuits 302 can be other than the cooling circuits for the respective legs of an A-coil assembly or V-coil assembly in a CRAC. For example, they could be cooling circuits of different CRACs, provided that they are identical and operate under the same conditions.

It should be understood that condensers 212 can be any of the heat rejection devices described above with regard to heat rejection device 124 of FIG. 1.

Controller 320 includes fault detection to detect whether there has been a failure of any of the cooling circuits 302 that it is controlling. In an aspect, the fault detection includes controller 320 monitoring the operating parameters of each of the cooling circuits 302 and comparing the operating parameters of one cooling circuit 302 to the operating parameters of the other cooling circuit 302. The operating parameters are the inputs and outputs of the cooling circuits, such as the sensor readings and control outputs to the controllable devices, such as the compressor, EEV, fans, and the like. They may include temperatures, pressures, fan speeds, EEV positions, compressor loading, and the like. In the schematic of FIG. 3, “T” in a circle indicates a temperature sensor and “P” in a circle indicates a pressure sensor.

Since the cooling circuits 302 are identical and are operating at similar if not identical conditions, the corresponding operating parameters of each of the cooling circuits 302 should not differ from each other by any appreciable amount. Conditions in this context means the application conditions in which the cooling system is applied, as would be appreciated by one of ordinary skill in the art. For example, for a cooling system having an air cooled condenser, the applications conditions are the indoor air flow, temperature and humidity of the indoor return air entering the cooling system, and temperature of outdoor air entering the outdoor condenser. For a water cooled condenser, the last condition would instead be a temperature of fluid entering the condenser and fluid % glycol entering the condenser. There would be other variations in application conditions for a water cooling chiller, etc., again as would be readily understood by one of ordinary skill in the art. In this regard, the monitored operating parameters of each of the cooling circuits that are used by controller in making the comparison are obtained at essentially the same time as at any given time, the cooling circuits will be operating at similar if not identical conditions. If controller 320 determines that the corresponding operating parameters for the cooling circuits 302 differ from each other by an appreciable amount, controller 320 determines that a fault has occurred. Controller 320 determines possible causes of the fault and outputs a response based on this determination. The response may include an alarm, adjustment to the maintenance schedule for cooling system 300, a message indicating the potential problem, or any combination of these. It should be understood that these are examples of responses and the responses can include other types of responses.

Controller 320 determines the possible causes of the fault based on the comparison of corresponding operating parameters of the cooling circuits 302, and which differ from each other by an appreciable amount and which do not. As used in this context, “appreciable amount” means a sufficient difference to indicate an alarm condition. It should be understood that different conditions could mean that there are different differences at which the alarm condition occurs. The appreciable amount will be a measurement difference of temperature, pressure, or percent of speed or capacity. The magnitude of the appreciable amount may be determined through experimentation, experience, sensor accuracy and/or percent of full scale reading. For example, they may be initially set broadly and then refined based on experiential data from systems in operation.

FIG. 4 is a spreadsheet showing an example of the foregoing fault detection listing various failure modes and the relationship of particular operating parameters on which each of the failure modes is determined. For example, with reference to FIG. 4, “Suct Press” in FIG. 4 stands for compressor suction pressure. A pressure difference is defined between the readings of the compressor suction pressures on the two systems at which to annunciate a warning and take action. This difference could, by way of example and not of limitation, be 10 psi for R-407C refrigerant systems and may be 20 psi for R-410A refrigerant systems. These can be fixed values or user adjustable values. The same approach is true for the other parameters listed in FIG. 4. The following table identifies the parameters listed in FIG. 4, but it should be understood that other parameters may also be usable.

Suct Press Compressor suction pressure (measured pressure) Suct Temp Compressor suction temperature (measured temperature) SH Refrigerant Superheat (could be at compressor suction or discharge) (calculated temperature) EEV Pos Electronic Expansion Valve Position (% open) Liqd Pressure Refrigerant liquid pressure (measured pressure) Liqd Temp Refrigerant liquid temperature (measured temperature) SC Refrigerant Subcooling (calculated temperature) Disc Temp Compressor discharge temperature (measured temperature) Cond Fan Speed Outdoor condenser fan speed (RPM or %) (measured speed) Digital % Digital compressor % of capacity (% setting of digital compressor) Outdoor amb. Outdoor ambient temperature (measured temperature)

In an aspect, in addition to comparing the corresponding operating parameters of the cooling circuits 302 to detect whether a fault has occurred, controller 320 may also use a comparison of the operating parameters of a cooling circuit 302 to a snapshot of the operating parameters of that cooling circuit taken after the cooling circuit is determined to be operating properly after start-up, which is referred to herein as the original snapshot. Controller 320 makes this comparison when the cooling circuit 302 is operating at a similar condition to when the original snapshot was taken.

It should be understood that the above described fault detection can be used with cooling systems having identical cooling circuits that are other than DX cooling circuits. For example, it can be used with cooling circuits that include both a DX mode and a pumped refrigerant economizer mode.

With reference to FIG. 5, an embodiment of a cooling system 500 having a plurality of cooling circuits 502 having a DX mode and a pumped refrigerant economizer mode is shown. Cooling system 500 includes a plurality of DX cooling circuits 502 with each cooling circuit 502 having an evaporator 504, expansion valve 506 (which may preferably be an electronic expansion valve but may also be a thermostatic expansion valve or fixed orifice), condenser 508 and compressor 510 arranged in a DX refrigeration circuit. Each cooling circuit 502 also includes a fluid pump 512, solenoid valve 514 and check valves 516, 518, 522. An outlet 562 of condenser 508 is coupled to an inlet 528 of pump 512 and to an inlet 530 of check valve 516. An outlet 532 of pump 512 is coupled to an inlet 534 of solenoid valve 514. An outlet 536 of solenoid valve 514 is coupled to an inlet 538 of electronic expansion valve 506. An outlet 540 of check valve 516 is also coupled to the inlet 538 of electronic expansion valve 506. An outlet 542 of electronic expansion valve 506 is coupled to a refrigerant inlet 544 of evaporator 504. A refrigerant outlet 546 of evaporator 504 is coupled to an inlet 548 of compressor 510 and to an inlet 550 of check valve 518. An outlet 552 of compressor 510 is coupled to an inlet 554 of check valve 522 and an outlet 556 of check valve 522 is coupled to an inlet 558 of condenser 508 as is an outlet 560 of check valve 518. The foregoing description of each cooling circuit 502 corresponds to the description of FIG. 12 of U.S. Ser. No. 13/446,310 for “Vapor Compression Cooling System with Improved Energy Efficiency Through Economization” filed Apr. 13, 2012. The entire of disclosure of U.S. Ser. No. 13/446,310 is incorporated herein by reference. In this regard, cooling circuits 502 can be any of the cooling circuits disclosed in U.S. Ser. No. 13/446,310 having both a DX mode and a pumped refrigerant mode, provided that the cooling circuits 502 are identical to each other.

Cooling system 500 also includes a controller 520 coupled to controlled components of cooling system 500, such as electronic expansion valve 506, compressor 510, pump 512, solenoid valve 514, condenser fan 524, and evaporator air moving unit 526. Controller 520 may include, or be coupled to, a user interface 521.

Controllers 320, 520 may illustratively be an iCOM® control system available from Liebert Corporation of Columbus, Ohio programmed with software implementing the above described fault detection.

FIG. 6 is a basic flow chart of a software program for controllers 320, 520 implementing the above described fault detection. For convenience, the following discussion refers to cooling circuits 302 and controller 320, but it should be understood that it also applies to cooling circuits 502 and controller 520. At 600, controller 320 monitors the operating parameters of cooling circuits 302. At 602, controller 320 compares corresponding operating parameters of the cooling circuits 302. As discussed above, the monitored operating parameters of each of the cooling circuits that are used by controller 320 in making the comparison are obtained at essentially the same time as at any given time, the cooling circuits will be operating at identical conditions. At 604, controller 320 determines whether a fault has occurred based on the comparison. If a fault has occurred, at 606 controller 320 determines the possible failure modes based on the relationship of certain corresponding operating parameters of the cooling circuits 302 and at 608, outputs an appropriate response. If at 604 controller 320 determined that a fault had not occurred, controller 320 returns to 600 as it does after outputting the appropriate response at 608.

In an aspect, controller 320 may use a comparison of the operating parameters of a cooling circuit 302 to a snapshot of the operating parameters of that cooling circuit taken after the cooling circuit is determined to be operating properly after start-up, which is referred to herein as the original snapshot. Controller 320 makes this comparison when the cooling circuit 302 is operating at a similar condition to when the original snapshot was taken. Similar in this context means that the application conditions are essentially the same, taking into account tolerances that may for example be heuristically determined. It should be understood that this aspect could be used in cooling systems having a single cooling circuit as well as a plurality of cooling circuits.

FIG. 7 is a basic flow chart of a software program for controller 320 implementing the above described fault detection in which a comparison to the original snapshot is used. At 700, controller 320 takes the original snapshot of each of cooling circuits 302. At 702, controller 320 monitors the operating parameters of cooling circuits 302. At 704, controller 320 checks whether a cooling circuit 302 is operating at a similar condition as it was operating when the original snapshot was taken. If so, at 706 controller 320 compares the current operating parameters of the applicable cooling circuit 302 to the original snapshot of the operating parameters of that cooling circuit 302 and then proceeds to 708. At 708, controller 320 determines whether a fault has occurred based on the comparison. It determines that a fault has occurred if current operating parameters differ from the operating parameters in the original snapshot by an appreciable amount. Upon determining that a fault has occurred, at 710 controller 320 determines possible causes of the fault. It does so in a similar fashion as described above with reference to FIG. 4 with the comparison being between the monitored operating parameters and original snapshot. At 712, controller 320 outputs a response based on this determination and then returns to 702. If at 704 no cooling circuit 302 was found to be operating at a similar condition as it was operating when the original snapshot was taken, or if at 708 controller 320 determined a fault had not occurred, controller 320 returns to 702.

In an aspect, controller 320 may use known operating parameters of the cooling circuit and calculate the remaining operating parameters, which are collectively referred to herein as the system model operating parameters. The known operating parameters can for example include control outputs that controller 320 determines and outputs and monitored inputs, such as sensor readings. The calculated operating parameters reflect what the operating parameters of the control circuit should be if the control circuit is operating properly. The controller then compares the monitored operating parameters of a cooling circuit 302 to the system model operating parameters. It should be understood that the monitored operating parameters can include control outputs as well as inputs such as sensor readings. As known by those of ordinary skill in the art, a system model is a mathematical model of a system typically implemented in software that mathematically calculates the system operating parameters. It typically uses a subset of known system operating parameters to calculate the remaining system operating parameters. As is understood by those of ordinary skill in the art of system modeling, a number of different combinations of known system operating parameters can be used with the system model to calculate the remaining system operating parameters. Here, the system model is a system specific model based on the combination of components that make up the specific cooling circuit. For example, using return air temperature, evaporator fan speed, compressor loading percentage and outdoor ambient temperature, the system model can calculate the capacity of the cooling circuit, temperatures and pressures at various points in the cooling circuit, power consumption, valve positions, and the like. The system model of the cooling circuit 302 may be pre-programmed into controller 320 or controller 320 could develop the system model based on historical operation of cooling circuit 302, similar to the snapshot approach discussed above. Controller 320 uses the system model to calculate the operating parameters of cooling circuit 302 and then compares these calculated operating parameters to the monitored operating parameters. Illustratively, controller 320 calculates the operating parameters on a real time basis as the monitored operating parameters are collected. It should be understood that this aspect could be used in cooling systems having a single cooling circuit as well as a plurality of cooling circuits.

Along the lines discussed above, controller 320 can use a number of different combinations of known operating parameters in the subset of operating parameters that it uses with the system model to calculate the remaining operating parameters of cooling circuit 302. If a fault is found, one of the ways the controller could potentially determine what the fault in cooling circuit 302 is, would be to calculate operating parameters of the cooling circuit 302 using the system model and several different combinations of known operating parameters to isolate what operating parameter is causing the discrepancy between the system model operating parameters and the monitored operating parameters. For example, if the return air temperature sensor reading is faulty (bad sensor) and it's used as an input into the system model, most of the monitored operating parameters, e.g., sensor inputs and control outputs will be different from the system model operating parameters. However, if the system model is then used to recalculate operating parameters using a different set of known system parameters that doesn't include the return air temperature sensor, then all of the system model operating parameters would match the monitored operating parameters except the return air temperature sensor. Controller 320 would then know that the return air temperature sensor is faulty.

FIG. 8 is a basic flow chart of a software program for controller 320 implementing the above described fault detection in which controller 320 calculates the operating parameters using a system model and compares the monitored operating parameters to the calculated operating parameters. At 800, controller 320 generates system model operating parameters by using known operating parameters of each of cooling circuits 302 to calculate the remaining operating parameters of the respective cooling circuit 302 using the system model of each cooling circuit 302. The known operating parameters used in the calculation and the calculated operating parameters are collectively the system model operating parameters as discussed above. At 802, controller 320 monitors the operating parameters of cooling circuits 302. At 804, controller 320 compares the current operating parameters of the applicable cooling circuit 302 to the calculated operating parameters of that cooling circuit 302 and then proceeds to 806. At 806, controller 320 determines whether a fault has occurred based on the comparison. It determines that a fault has occurred if the monitored operating parameters differ from the calculated operating parameters by an appreciable amount. Upon determining that a fault has occurred, at 808 controller 320 determines possible causes of the fault. It may do so in a similar fashion as described above with reference to FIG. 4 with the comparison being between the monitored operating parameters and system model operating parameters. It may also do so as described above using different combinations of known operating parameters as inputs to calculate operating parameters using the system model. At 810, controller 320 outputs a response based on this determination and then returns to 800. If at 806 controller 320 determined a fault had not occurred, controller 320 returns to 800. It should be understood that controller 320 may not need to calculate the operating parameters using the system model each time it executes the software routine shown in FIG. 8. For example, if the known operating parameters that are used in the system model in the calculation of the remaining operating parameters have remained essentially the same, then controller 320 may dispense with the step of calculating the remaining operating parameters and use the most recent set of system model operating parameters.

It should be understood that when it is stated herein that controller 320 performs a particular function, it means that controller 320 is configured with appropriate software, electronic logic, or both, to perform that function. For example, if controller 320 is a programmable device, controller 320 is programmed with specific software to perform the function.

As used herein, the term controller, control module, control system, or the like may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; a programmable logic controller, programmable control system such as a processor based control system including a computer based control system, a process controller such as a PID controller, or other suitable hardware components that provide the described functionality or provide the above functionality when programmed with software as described herein; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor.

The term software, as used above, may refer to computer programs, routines, functions, classes, and/or objects and may include firmware, and/or microcode.

The apparatuses and methods described herein may be implemented by software in one or more computer programs executed by one or more processors of one or more controllers. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A method of fault detection in a cooling system having a plurality of identical cooling circuits and a controller that controls the cooling circuits, the method comprising: monitoring with the controller operating parameters of each of the cooling circuits the controller is controlling and determining with the controller that a fault has occurred when corresponding monitored operating parameters of the cooling circuits obtained at essentially the same time differ from each other by an appreciable amount.
 2. The method of claim 1 including determining with the controller possible causes of a fault that occurred based on a comparison of corresponding operating parameters of the cooling circuits and which differ from each other by an appreciable amount and which do not.
 3. The method of claim 2 including outputting with the controller a response based on the determined possible causes of the fault.
 4. A cooling system having a plurality of identical cooling circuits, comprising: a controller configured to control the cooling circuits, the controller configured to include fault detection to detect whether there has been a failure of any of the cooling circuits it is controlling; and the fault detection includes the controller configured to monitor operating parameters of each of the cooling circuits it is controlling and determine that a fault has occurred if corresponding monitored operating parameters of the cooling circuits obtained at essentially the same time differ from each other by an appreciable amount.
 5. The cooling system of claim 4 wherein the controller is configured to determine that a fault has occurred if corresponding operating parameters of the cooling circuits differ from each other by an appreciable amount.
 6. The cooling system of claim 5 wherein the controller is configured to determine possible causes of a fault that occurred based on a comparison of corresponding operating parameters of the cooling circuits and which differ from each other by an appreciable amount and which do not.
 7. The cooling system of claim 6 wherein the controller is configured to output a response based on the determined possible causes of the fault.
 8. A method of fault detection in a cooling system having a controller that controls a cooling circuit of the cooling system, the method comprising: monitoring with the controller operating parameters of the cooling circuit; and determining with the controller that a fault has occurred in the cooling circuit when the monitored operating parameters of the cooling circuit differ by an appreciable amount from corresponding operating parameters in an original snapshot of the operating parameters of the cooling circuit taken when the cooling circuit was operating properly, and making this determination with the controller using the monitored operating parameters for the cooling circuit when the cooling circuit was operating at a similar condition to a condition that the cooling circuit was operating when the original snapshot was taken.
 9. The method of claim 8 including determining with the controller possible causes of a fault that occurred based on a comparison of corresponding operating parameters of the monitored operating parameters of the cooling circuit and the operating parameters in the original snapshot and which differ from each other by an appreciable amount and which do not.
 10. The method of claim 9 including outputting with the controller a response based on the determined possible causes of the fault.
 11. A cooling system, comprising: a cooling circuit and a controller configured to control the cooling circuit; the controller configured to include fault detection to detect whether there has been a failure of the cooling circuit; and the fault detection includes the controller configured to monitor operating parameters of the cooling circuit and determine that a fault has occurred if the monitored operating parameters of the cooling circuit differ by an appreciable amount from corresponding operating parameters in an original snapshot of the operating parameters of that cooling circuit taken when the cooling circuit was operating properly, the controller configured when making this determination using the monitored operating parameters for the cooling circuit when the cooling circuit was operating at a similar condition to a condition that the cooling circuit was operating when the original snapshot was taken.
 12. The cooling system of claim 11 wherein the controller is configured to determine possible causes of a fault that occurred based on a comparison of corresponding operating parameters of the monitored operating parameters of the cooling circuit and the operating parameters in the original snapshot and which differ from each other by an appreciable amount and which do not.
 13. The cooling system of claim 12 wherein the controller is configured to output a response based on the determined possible causes of the fault.
 14. A method of fault detection in a cooling system having a controller that controls a cooling circuit of the cooling system, the method comprising: using known operating parameters of the cooling circuit and calculating with a controller using a system model of the cooling circuit remaining operating parameters of the cooling circuit with the known operating parameters and the calculated operating parameters collectively system model operating parameters; monitoring with the controller operating parameters of the cooling circuit; and determining with the controller that a fault has occurred in the cooling circuit when the system model operating parameters differ by an appreciable amount from corresponding monitored operating parameters.
 15. The method of claim 14 including determining with the controller possible causes of a fault that occurred based on a comparison of corresponding operating parameters of the monitored operating parameters of the cooling circuit and the system model operating parameters and which differ from each other by an appreciable amount and which do not.
 16. The method of claim 15 including outputting with the controller a response based on the determined possible causes of the fault.
 17. The method of claim 14 including using a plurality of different combinations of known operating parameters of the cooling circuit in calculating with the controller remaining operating parameters of the cooling circuit to generate a plurality of sets of system model operating parameters and determining with the controller possible causes of a fault that occurred based on comparisons of corresponding operating parameters of the monitored operating parameters of the cooling circuit and the system model operating parameters in the plurality of sets of system model operating parameters and which differ from each other by an appreciable amount and which do not.
 18. The method of claim 17 including outputting with the controller a response based on the determined possible causes of the fault.
 19. A cooling system, comprising: a cooling circuit and a controller configured to control the cooling circuit; the controller configured to include fault detection to detect whether there has been a failure of the cooling circuit; and the fault detection includes the controller configured to use known operating parameters of the cooling circuit and calculating using a system model of the cooling circuit remaining operating parameters of the cooling circuit with the known operating parameters and the calculated operating parameters collectively system model operating parameters; and the controller configured to monitor operating parameters of the cooling circuit and determining that a fault has occurred if the system model operating parameters differ by an appreciable amount from corresponding monitored operating parameters.
 20. The cooling system of claim 19 wherein the controller is configured to determine possible causes of a fault that occurred based on a comparison of corresponding operating parameters of the monitored operating parameters of the cooling circuit and the system model operating parameters and which differ from each other by an appreciable amount and which do not.
 21. The cooling system of claim 20 wherein the controller is configured to output a response based on the determined possible causes of the fault.
 22. The cooling system of claim 19 wherein the controller is configured to use a plurality of different combinations of known operating parameters of the cooling circuit in calculating remaining operating parameters of the cooling circuit to generate a plurality of sets of system model operating parameters and the controller is configured to determine possible causes of a fault that occurred based on comparisons of corresponding operating parameters of the monitored operating parameters of the cooling circuit and the system model operating parameters in the plurality of sets of system model operating parameters and which differ from each other by an appreciable amount and which do not.
 23. The cooling system of claim 22 wherein the controller is configured to output a response based on the determined possible causes of the fault. 